The hospital-room questioning of the surviving suspect in the Boston Marathon bombings is generating concern about whether he should have been interrogated without first being told of his constitutional rights to silence and a lawyer — and, conversely, whether federal agents actually should have had more time with him before he was read his rights.

Dzhokhar Tsarnaev faced 16 hours of questioning before he was advised of his Miranda rights, and investigators say he told them of his role in the two bombings near the Boston Marathon finish line on April 15. He explained that he and his brother, Tamerlan, were angry about the U.S. wars in Afghanistan and Iraq and the killing of Muslims there, according to two U.S. officials who spoke on condition of anonymity because they weren’t authorized to discuss the case with reporters.

He also described a spur-of-the-moment plan that the brothers hatched to drive to New York and set off their remaining explosives there, New York City officials said Thursday.

In Boston, federal agents invoked an exception to the Miranda warnings that allows for questioning when public safety may be threatened. But they knew their time with Tsarnaev in the absence of a lawyer would be limited.

On Sunday, prosecutors filed a criminal complaint charging Tsarnaev with a role in the bombings. That action led directly to the improvised court hearing in the hospital the following morning at which U.S. Magistrate Judge Marianne Bowler told Tsarnaev he did not have to answer questions and could have a lawyer.

And he apparently did stop, though other cases in recent years suggest that silence won’t necessarily last.

Could that first hearing on Monday have been delayed?

The hearing is supposed to take place “without unnecessary delay,” according to the federal rules, sometimes within a matter of hours.

The rules governing such hearings, known as an initial appearance, require the judge to tell a defendant of his rights, Justice Department spokesman Dean Boyd said. “The prosecutors and FBI agents in Boston were advised of the scheduled initial appearance in advance of its occurrence.”

Civil liberties advocates have said a suspect should rarely be questioned without a lawyer and without being told he doesn’t have to respond.

“Miranda rights are an incredibly important civil liberties safeguard,” said Hina Shamsi of the American Civil Liberties Union. “The public safety exception must be read narrowly, as it has been by the courts.”

But California Democratic Rep. Adam Schiff, a former federal prosecutor, said he has questions about how the court proceeding came about.

“I would have thought the public exception rule would have allowed more time for the questioning of the suspect prior to the arraignment and/or advising of rights,” Schiff said.

A fellow Democrat, Sen. Carl Levin of Michigan, agreed that some questions remain about when the judge arrived and whether she interrupted questioning. But, Levin said, “we do know there was 16 hours of questioning and that they got very detailed information.”

Withholding a criminal suspect’s Miranda rights becomes a legal issue only if authorities try to use what they learned during the questioning.

In fact, prosecutors probably will want to introduce Tsarnaev’s confession as evidence against him.

“Prosecutors always prefer to have a confession,” said Tamar Birckhead, a former federal defender in Boston who now teaches law at the University of North Carolina. She predicted there would be a protracted legal battle over Tsarnaev’s statements, if his case comes to trial and prosecutors say they intend to use them.

But other legal experts said any controversy over those early statements should not obscure the rest of the government’s case.

“When you read the affidavit, it lays out the evidence the FBI gathered wholly apart from any statements he made to law enforcement. Based on my experience, that’s a pretty strong case, even without statements made by the defendant to law enforcement directly,” said former federal prosecutor Juliet Sorensen, a Northwestern University law professor.

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